"Niggers say a drowned man’s shadow was watching for him in the water all the time."
Shadow in river
Creative Commons AttributionShadow in river - Credit: srbyug

According to James Frazer’s The Golden Bough (1890), cultures as diverse as Melanesia, South Africa, ancient India and ancient Greece have believed a person’s reflection in water to be his or her soul. As an external manifestation, this reflection-soul was vulnerable to water-spirits who might wrest it away and leave the body to perish. Looking into water was therefore regarded as taboo and to dream of one’s own reflection was seen as an omen of death. It seems likely that this is the origin of the folk belief to which Quentin refers.